Glass fibers are conventionally formed by the attenuation of molten glass through orifices in a bushing by mechanical means. One of the ways of forming the molten glass above the bushing orifices is to supply marbles of glass having the desired composition to a pre-melter above the bushing orifices. The marbles are heated to a temperature above their melting point and the molten glass is held in the bushing until it is attenuated into fibers. Typical systems for feeding glass marbles directly to the pre-melter are those illustrated in U.S. Pat. Nos. 2,453,864; 2,687,599; 3,875,893; 3,013,096; 3,103,361; 3,049,754; 3,056,846; 3,104,761 and 3,701,642. With the exception of U.S. Pat. No. 2,687,599 and U.S. Pat. No. 3,779,730 which will be more fully discussed below, all of these patents must either vibrate the feed system or force-feed or drop marbles into the system in order to maintain a constant supply of marbles to the pre-melter.
In U.S. Pat. No. 2,687,599 gravity flow of glass marbles from a marble supply to a pre-melter is utilized. The marbles run along a plurality of tubular cylindrical tracks which are slightly in excess of the diameter of the marbles to a mechanism for dropping marbles one by one into the pre-melter.
In U.S. Pat. No. 3,779,730 a single line of marbles flow by gravity from a hopper to a pre-melter. Recognizing the tendency for such a system to become clogged, this patent includes an alarm system for determining clogs and warning the operator of these occurrences.
While the prior art systems may be utilized to feed marbles to a marble melt bushing, these systems do encounter problems. Thus, when an oversized marble gets into these conveyor systems, blockage of the system often results. When any such system is blocked, it becomes necessary to manually remove the oversized blocking marble from the system. Often this removal involves stopping production while the impediment is being removed.
A second problem common to the prior art systems is the fact that glass marbles have a tendency to chip and break. As these chips enter the feed systems of the prior art along with full sized marbles, the flow of marbles may be stopped with the resulting necessity of manually clearing the blockage.
A third problem which occurs, even when only correctly sized glass marbles are employed, is a tendency for the marbles to bridge among themselves in the conveying system. In simpler terms, glass marbles have a tendency to plug up a passage rather than to flow through the passage evenly. This again results in an interruption in flow of the marble in the feed system with the same necessity for manual clearance.
In another system, marbles are gravity fed vertically from hoppers to the pre-melter and bushing. However, realizing that the weight of the marbles on the bushing has an adverse effect on fiber production, the marbles are, in at least one embodiment, fed to a "pre-pre-melter," which melts the marbles and allows only molten glasss to the pre-melter and bushing. Such a system involves extra heating means, precious metal, and, of course, added costs. Typical of such systems are U.S. Pat. No. 3,056,846 and U.S. Pat. No. 3,730,695.
As can be readily seen, the prior art marble feed systems require an almost constant need for supervision to prevent interruptions and to clear blockages that do occur in the marble feed system or require intricately controlled feeds involving complicated apparatus.
The present invention eliminates the necessity for a constant watch over the marble melt feeding of a bushing and allows for the continuous feed of broken and oversized marbles along with the properly sized marbles to a pre-melter. The system is easy to construct and has no moving parts. Other advantages of the present invention will become apparent to those of ordinary skill in the art.